The present invention relates to a device having an attractive and poisonous action for combatting insects, and more particularly concerns a device which both releases pheromones and develops an insecticide action, and by the use of which device it is possible to attract and eliminate adult insects.
For the past ten years pheromones have gained great importance in the field of research for new methods for controlling species of insects noxious to agricultural cultivations; when compared to conventional products, said substances have the advantage of offering a considerable selectivity towards one specific or a limited number of kindred species of insects, without thereby involving the harmless or even useful fauna.
It is thus possible to fight a certain parasite with the help of pheromones without thereby disturbing the surrounding ecological equilibrium.
The pheromones are secreted towards the outside of the body of the insects by special glands and, according to the type of reaction they induce, they may be subdivided into: aggregating, tracing, alarming or warning, sexually attracting, etc., hormones. The most diffused and most interesting for the possibilities they offer for the control of the noxious species of insects are the sexual pheromones which are secreted by the female, but in a number of species also by the male insect, and which attract the individuals of the opposite sex for the mating. Small quantities of such attractive pheromones obtained by synthesis awake the same reactions that are induced in the insects by the natural hormone.
The synthetic sexual pheromones are used both for watching the growth of the parasite populations and for directly controlling the noxious species by hindering the matings.
The first type of application (monitoring) allows to follow, by means of periodical drawings or samplings of the captured insects by special traps, the fluctuations of the parasite populations by watching their biological cycle and by forecasting the possible attainment of the "threshold of noxiousness".
On the basis of these data it is then possible to decide the opportunity and the moment for intervening with pesticides.
In the second type of application, the sexual pheromones may partially substitute or totally replace the insecticides and directly control the noxious species by interfering with their reproductive activity.
The techniques used for this purpose are two: the massive capture and the disorienting. The first consists in attracting and thus in capturing the greatest possible number of adult insects by means of special traps baited with the pheromone.
The second technique is realized by diffusing the attracting agent through the air in such a way as to hinder the insects in localizing the individuals of the opposite sex, thus hindering the matings.
The diffusion of the pheromone may be obtained by placing the product in various distinct and suitably distanced points of the cultivation to be protected, or by distributing the product uniformly over the whole area of interest. In the first case, there are used dispensers in which the active principle is incorporated in substrates of a different nature which control the releasing speed and the persistence. In the second case, there are used special formulations with a regulated releasing rate, which are applied from the ground or from the air.
Conceptually, the two systems of pheromone diffusion differ from one another inasmuch as, in the case of the localized dispensers, these simulate the recalling insect, thereby creating numerous false traces, while the uniformly diffused pheromone covers up the natural recalls of the insects thereby hindering their perception on the part of the individuals.
The first system is realized, for instance, with capillaries with an open end through which the active principle volatilizes (U.S. Pat. No. 4,017,030) while the second system is realized by microcapsules with polyamide walls (U.S. Pat. No. 3,577,515) or by a gel or jelly (U.S. Pat. No. 2,800,457 and U.S. Pat. No. 2,800,458) or again by special mixtures of absorbing and adsorbing powders (see U.S. Pat. No. 4,325,941).
These systems are used in the fight against parasites but allow to obtain satisfactory results only for a few species of insects and only in particular situations. In fact, if, for instance, the insects to be controlled are very mobile and their number is very high, there will be a considerably high probability of casual approaches between the individuals with a consequent loss of efficacy of the method.
Said risk may be reduced by increasing the number of the localized dispensers or the concentration of the uniformly distributed pheromone. Both solutions involve, however, an increased economical burden.